Image pickup apparatus, image pickup method , and image pickup control program
When flash photography is performed, an exposure time at the time of the preliminary light emission of a flash is set as short as possible so that the appropriate amount of light required for the main light emission of the flash can be accurately computed regardless of the amount of external light. Before the main light emission of the flash, an exposure operation prior to preliminary light emission and an exposure operation at the time of preliminary light emission are performed. When the exposure operation prior to preliminary light emission is performed, after the exposure operations of all pixels included in a solid-state image pickup device have been simultaneously started at a time T91, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals at a time T92. When the exposure operation at the time of preliminary light emission is performed, after the exposure operations of all the pixels included in the solid-state image pickup device have been simultaneously started at a time T94, the preliminary light emission of the flash is performed. The pixel signals of individual pixels are intermittently read out at predetermined pixel intervals at a time T95. Subsequently, the brightness levels of images captured in the exposure operation prior to preliminary light emission and the exposure operation at the time of preliminary light emission are individually detected on the basis of the signals of the captured images. The amount of light required for the main light emission of the flash is computed on the basis of a difference detection value that is the difference between the brightness levels.
The present invention relates to image pickup apparatuses, image pickup methods, and image pickup control programs for capturing an image using a solid-state image pickup device in which the pixel signals of individual pixels can be randomly accessed, and, more particularly, to an image pickup apparatus, an image pickup method, and an image pickup control program capable of capturing an image using a flash.
BACKGROUND ARTImage pickup apparatuses fire a flash so as to adjust the amount of light when capturing an image of a subject under low illuminance conditions. Some image pickup apparatuses that capture an image using a solid-state image pickup device have a function of performing preliminary light emission using a flash and detecting and analyzing the amount of light reflected from a subject to calculate the appropriate amount of light required for main light emission.
CCD (Charge Coupled Device) image sensors have been mostly used as an image pickup device for an image pickup device. However, as the number of pixels included in a solid-state image pickup device becomes increased, CMOS (Complementary Metal Oxide Semiconductor) image sensors are currently attracting attention. A CMOS image sensor has features in which pixel signals can be randomly accessed and can be rapidly read out compared with a CCD image sensor and it has high sensitivity and consumes low power.
However, in known image pickup apparatuses using a CMOS image sensor, reflected light caused by preliminary light emission of a flash is transmitted to only a part of the whole area of a solid-state image pickup device, since exposure times of individual pixels are different from each other. Accordingly, it is difficult to accurately calculate the amount of light required for main light emission. In order to overcome this difficulty, there is an image pickup apparatus in which a part of the whole area of a solid-state image pickup device is set as a metering area and preliminary light emission is performed during the electric charge storage time of photoelectric conversion elements included in the metering area to allow the metering area to accurately receive reflected light caused by the preliminary light emission (see, for example, Japanese Unexamined Patent Application Publication No. 2000-196951 (paragraphs [0018] to [0026] and FIG. 2).
DISCLOSURE OF INVENTIONHowever, in such an image pickup apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2000-196951, a long exposure time must be set so as to allow the photoelectric conversion elements included in the metering area to simultaneously receive the reflected light caused by the preliminary light emission. Accordingly, if the preliminary light emission is performed when external light is strong, the amount of light input into a certain area of the CMOS image sensor may exceed the dynamic range thereof. Consequently, the amount of light actually received by the area of the CMOS image sensor cannot be detected, and it is therefore difficult to precisely calculate the amount of light required for main light emission.
The present invention has been made in view of the above-described background. An object of the present invention is to provide an image pickup apparatus capable of precisely computing the appropriate amount of light required for main light emission regardless of the intensity of external light by shortening the exposure time of preliminary light emission as much as possible in flash photography.
Furthermore, another object of the present invention is to provide an image pickup method capable of precisely computing the appropriate amount of light required for main light emission regardless of the intensity of external light by shortening the exposure time of preliminary light emission as much as possible in flash photography.
Still furthermore, another object of the present invention is to provide an image pickup control program capable of precisely computing the appropriate amount of light required for main light emission regardless of the intensity of external light by shortening the exposure time of preliminary light emission as much as possible in flash photography.
According to an embodiment of the present invention, there is provided an image pickup apparatus for capturing an image using a solid-state image pickup device in which the pixel signals of individual pixels can be randomly accessed. The image pickup apparatus includes: a flash for exposing a subject to light; detecting means for detecting the brightness level of a captured image from an image signal obtained by the solid-state image pickup device; and controlling means for causing the flash to perform preliminary light emission prior to the main light emission of the flash, causing the solid-state image pickup device to capture an image at the time of the preliminary light emission, causing the detecting means to detect the brightness level of the image captured at the time of the preliminary light emission on the basis of the signal of the captured image, and computing the amount of light required for the main light emission of the flash on the basis of the detected brightness level at the time of the preliminary light emission. The controlling means intermittently reads out the pixel signals of individual pixels at predetermined pixel intervals after causing the solid-state image pickup device to simultaneously start the exposure operations of all pixels included therein at the time of the preliminary light emission, and then transmits the read out pixel signals to the detecting means.
In such an image pickup apparatus, the preliminary light emission of a flash is performed prior to the main light emission thereof so as to capture an image. The amount of light required for the main light emission of the flash is computed on the basis of the detection result of the brightness level of the captured image. When the preliminary light emission is performed, after the exposure operations of all pixels included in a solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals. Consequently, the effect of the preliminary light emission is applied to the whole image area of the solid-state image pickup device. In addition, the exposure time of the solid-state image pickup device at the time of the preliminary light emission is shortened, and the detected amount of the component of external light is decreased.
According to an embodiment of the present invention, there is provided an image pickup method of capturing an image by firing a flash using a solid-sate image pickup device in which the pixel signals of individual pixels can be randomly accessed. The image pickup method includes: an image capturing step at the time of preliminary light emission of causing the flash to perform preliminary light emission prior to the main light emission of the flash, and causing the solid-state image pickup device to capture an image at the time of the preliminary light emission; a detecting step at the time of preliminary light emission of causing detecting means to detect the brightness level of the image captured at the time of the preliminary light emission; and a computing step of causing computing means to compute the amount of light required for the main light emission of the flash on the basis of the brightness level detected at the time of the preliminary light emission. In the image capturing step at the time of preliminary light emission, after the exposure operations of all pixels included in the solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals.
In such an image pickup method, the preliminary light emission of a flash is performed prior to the main light emission thereof so as to capture an image. The amount of light required for the main light emission of the flash is computed on the basis of the detection result of the brightness level of the captured image. When the preliminary light emission is performed, after the exposure operations of all pixels included in a solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals. Consequently, the effect of the preliminary light emission is applied to the whole image area of the solid-state image pickup device. In addition, the exposure time of the solid-state image pickup device at the time of the preliminary light emission is shortened, and the detected amount of the component of external light is decreased.
An embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The image pickup apparatus shown in
The lens 11 focuses reflected light incident from a subject onto the light-receiving surface of the image pickup device 13. The iris 12 changes the aperture thereof so that the amount of light received through the lens 11 can be suitable for the sensitivity of the image pickup device 13, and, in addition, has a shutter function. The image pickup device 13 includes a plurality of pixels on each of which an R, G, or B color filter is disposed, and photoelectrically converts light transmitted through the lens 11 to the pixels into analog image signals (electric charges). In addition, the image pickup device 13 is configured with an XY address type image sensor such as a CMOS image sensor in which the exposure operations and read-out operations of a plurality of pixels are individually performed at different times.
The AGC circuit 14 amplifies an image signal generated by the image pickup device 13. The A/D conversion circuit 15 converts the analog image signal amplified by the AGC circuit 14 into a digital image signal. The camera signal processing circuit 16 performs various pieces of signal processing upon the digital image signal converted by the A/D conversion circuit 15, and is provided with, for example, a white balance control circuit, a YC separation circuit, a filter circuit, an aperture controller, a gamma correction circuit, etc. (not shown). Although not shown in this drawing, the image signal output from the camera signal processing circuit 16 is transmitted to, for example, a display unit for displaying a captured image on a monitor, and a recording unit for encoding the image signal into a predetermined data format and recording data on the captured image onto a recording medium such as memory card. The detection circuit 17 detects the brightness level and color distribution of the area of the captured image on the basis of the image signal processed by the camera signal processing circuit 16. An integrated value of brightness signals of individual pixels included in the area of the captured image is used as a detection value representing a brightness level.
The system control unit 18 is configured with, for example, a micro-computer, and centrally controls individual units included in this image pickup apparatus on the basis of the brightness level and color distribution detected by the detection circuit 17 and the image signal processed by the camera signal processing circuit 16. For example, the system control unit 18 computes an exposure timing control signal for controlling an exposure operation and a read-out operation which are performed on each pixel included in the image pickup device 13, a gain control signal for controlling the gain of the AGC circuit 14, an optical block control signal for controlling the focus of the lens 11 and the aperture of the iris 12 via the driver 22, a flash control signal for controlling the firing operation of the flash 21 via the driver 20, etc., and outputs the computed control signals. The memory 19 stores the control data computed by the system control unit 18.
The driver 20 drives the flash 21 in accordance with the flash control signal computed by the system control unit 18 when flash photography is performed. The flash 21 is fired in accordance with a driving signal transmitted from the driver 20. The driver 22 drives the lens 11 and the iris 12 in accordance with the lens control signal computed by the system control unit 18. The memory 23 temporarily stores the image signal processed or being processed by the camera signal processing circuit 16.
The basic operation of this image pickup apparatus when a still image is captured is as follows.
First, before a user performs an image capturing operation, light received by the image pickup device 13 is photoelectrically converted into image signals, and the image signals are sequentially provided for the AGC circuit 14. The image signals are amplified by the AGC circuit 14 as appropriate, and are converted into digital signals by the A/D conversion circuit 15, and undergo various pieces of image quality correction processing in the camera signal processing circuit 16. The processed image signals are output to the display unit (not shown) to display a camera-through image on a monitor. Consequently, the user can adjust a field angle by checking the monitor.
In the above-described condition, if the user presses a release button (not shown), the system control unit 18 outputs control signals to the driver 22 and the image pickup device 13 so as to operate a shutter, whereby image signals of one frame are output from the image pickup device 13. At that time, the system control unit 18 outputs control signals to the lens 11, the iris 12, the image pickup device 13, and the AGC circuit 14 on the basis of the results of various pieces of processing performed by the camera signal processing circuit 16 and the detection result of the detection circuit 17 so as to appropriately control a focus, an exposure time, and the amount of light exposure.
The camera signal processing circuit 16 performs image quality correction processing upon the image signals of one frame provided via the AGC circuit 14 and the A/D conversion circuit 15 from the image pickup device 13, and outputs the processed image signals to the recording unit (not shown). Consequently, the image signals of one frame are encoded to generate a still image data file, and the generated data file is recorded onto a recording medium such as a memory card.
In addition, this image pickup apparatus can automatically fire the flash 21 in accordance with, for example, a user's operation or on the basis of the detection result of the detection circuit 17 at the time of image capturing. As described later, when flash photography is performed, preliminary light emission is performed immediately before the main light emission of the flash 21 under the control of the system control unit 18. The image signals of a captured image acquired from the preliminary light emission are detected by the detection circuit 17, and the amount of light required for the main light emission of the flash 21 is controlled on the basis of the detection results so that an appropriate captured image can be obtained.
In the image pickup device 13 according to this embodiment, individual pixels corresponding to photoelectric conversion elements can be randomly accessed. In the following, the description of this embodiment will be made using a CMOS image sensor as the image pickup device 13, and contrasting the CMOS image sensor with a widely used CCD image sensor when appropriate.
First, the basic configuration of the image pickup device 13 will be described.
As shown in
When the CCD image sensor is exposed to light, light incident on each of the light-receiving units 31 is photoelectrically converted into an electric charge. Each of the light-receiving units 31 stores an electric charge corresponding to the amount of incident light. When an electric charge transfer instruction signal is provided for the CCD image sensor, the electric charges stored in all of the light-receiving units 31 are simultaneously transferred to the corresponding vertical transfer registers 32. The electric charges transferred to the vertical transfer registers 32 are vertically transferred to the horizontal transfer register 33 in units of pixels (rows). The pixel signals included in individual rows which have been transferred to the horizontal transfer register 33 are horizontally transferred and output in units of pixels. At that time, since the vertical transfer registers 32 and the horizontal transfer register 33 are light-shielded, the amounts of electric charge transferred to these registers are kept constant.
On the other hand, as shown in
With increasing number of pixels included in an image pickup device, pixel pitch decreases. Even in this case, however, a configuration that realizes a relatively wide dynamic range of pixel signals, and a configuration allowing only necessary pixel signals to be arbitrarily read out in an image pickup device having many pixels are required. A CMOS image sensor has the advantage of being able to achieve the above-described configurations. In contrast, pixels included in the same column cannot be simultaneously read out in a CMOS image sensor, and an exposure operation and a read-out operation which are performed on each pixel are therefore complicated as described in the following.
In the CCD image sensor, as shown in
On the other hand, in the CMOS image sensor, while a pixel signal is read out from a certain pixel, other pixels store electric charges under the effect of external light, since the CMOS image sensor does not have components corresponding to the vertical transfer registers 32. Accordingly, as shown in
Next, a flash photography operation will be described.
In a still image capturing mode, when a shutter release button is pressed (step S31), the process proceeds from step S32. Here, if an operation mode in which a flash is automatically fired is set, the detection circuit 17 detects the integrated value of brightness signals included in image signals acquired by the image pickup device 13. The system control unit 18 detects the intensity of external light on the basis of the integrated value of the brightness signals, and determines whether the flash should be fired on the basis of the result of the detection (step S32). If it is determined that the external light is bright, the process proceeds to step S33. In step S33, normal image capturing in which the flash 21 is not fired is performed, and then the process ends. On the other hand, if it is determined that the external light is dark in step S32, the process proceeds to step S34 in which flash photography is performed. If an operation mode in which flash photography is performed regardless of the intensity of external light is set, the process proceeds to step S34 regardless of the determination result of step S32, and then flash photography is performed.
When flash photography is performed, first, the aperture and open time of the iris 12, the exposure time (shutter speed) of the image pickup device 13, and the gain of the AGC circuit 14 are set (step S34). It is desirable that the aperture of the iris 12 be set so as not to allow the amount of light incident from a nearby subject to exceed the dynamic range of the image pickup device 13 when the preliminary light emission of the flash 21 is performed. The preliminary light emission is performed so as to compute the amount of light required for main light emission. If the amount of light incident on the image pickup device 13 exceeds the dynamic range thereof, a distorted (saturated) image signal is acquired. Accordingly, the amount of light required for main light emission cannot be accurately computed. Furthermore, it is desirable that the exposure time of the image pickup device 13 be set as short as possible. If the exposure time becomes long, the effect of external light is increased, and the dynamic range used to detect the amount of light caused by the preliminary light emission is degraded. Consequently, the accuracy of the computation of the amount of light required for main light emission is decreased. Still furthermore, it is desirable that the gain of the AGC circuit 14 be set low so as to reduce the effect of image signal noise.
Subsequently, the image pickup device 13 performs an exposure operation and a read-out operation without causing the flash 21 to be fired before preliminary light emission is performed in the state in which the above-described aperture, exposure time, and gain settings are maintained. Subsequently, the detection circuit 17 detects the integrated value of brightness signals included in image signals acquired by the image pickup device 13, and stores the integrated value in the memory 19 as a detection value prior to preliminary light emission (D1) (step S35). This detection value prior to preliminary light emission D1 represents a detection value acquired under only external light without preliminary light emission.
Subsequently, preliminary light emission is performed by the flash 21 in accordance with the predetermined amount of light in the state in which the above-described aperture, exposure time, and gain settings are maintained (step S36). Subsequently, the image pickup device 13 performs an exposure operation and a read-out operation. The detection circuit 17 detects the integrated value of brightness signals included in the image signals acquired by the image pickup device 13, and stores the integrated value in the memory 19 as a detection value at the time of preliminary light emission (D2) (step S37). This detection value at the time of preliminary light emission D2 represents a detection value acquired under light including external light and light caused by the preliminary light emission.
Subsequently, the system control unit 18 reads out the detection value at the time of preliminary light emission D2 and the detection value prior to preliminary light emission D1 from the memory 19, and computes a difference detection value by subtracting the detection value prior to preliminary light emission D1 from the detection value at the time of preliminary light emission D2 (step S38). The difference detection value represents a detection value acquired under only the light caused by the preliminary light emission except for the external light. Subsequently, the system control unit 18 computes the amount of light required for main light emission to be performed by the flash 21 on the basis of the difference detection value (step S39). The flash 21 is fired in accordance with the computed amount of light, whereby flash photography is performed (step S40).
Thus, in an image pickup apparatus according to this embodiment, the preliminary light emission for flash photography has two stages. In one stage, the image signal read-out operation is performed in the state in which the flash is not fired, so that the detection value prior to preliminary light emission D1 is acquired. In another stage, the image signal read-out operation is performed after the flash has been fired, so that the detection value at the time of preliminary light emission D2 is acquired. The effect of external light is removed by subtracting the detection value prior to preliminary light emission D1 from the detection value at the time of preliminary light emission D2, whereby the amount of light required for main light emission can be accurately computed. Here, it is desirable that a time taken by the image pickup device 13 to perform the exposure operation prior to the preliminary light emission in step S35 and a time taken by the image pickup device 13 to perform the exposure operation at the time of the preliminary light emission in step S37 be as short as possible. Although flash photography is generally performed under low illuminance conditions, there is almost always some external light. For example, flash photography is also performed so as to highlight a backlit dark subject. Thus, in the case of strong external light, a suitable detection value, in particular, the suitable detection value at the time of preliminary light emission D2 cannot be acquired under the effect of the strong external light, and therefore a suitable difference detection value may not be acquired as described in the following with reference to
As shown in
As shown in
On the other hand, as shown in
Next, the timing of preliminary light emission for flash photography will be described. First, known flash photography will be described.
As shown in
On the other hand,
As shown in
In order to overcome this difficulty, as shown in
As shown in
However, pixel signals cannot be simultaneously read out from all the pixels included in the image area. A pixel signal read-out timing is shifted row by row. Accordingly, the exposure period of pixels included in a lower row is longer than that of pixels included in an upper row when the exposure operations prior to and at the time of preliminary light emission are performed. For example, as shown in
Here, it is assumed that a time taken to read out electric charges from all pixels is a single vertical synchronization period as shown in
In the example of
In such a case, the value of a synthesis of the component of external light and the component of reflected light caused by the preliminary light emission (the detection value at the time of preliminary light emission D2) is detected at the time of the preliminary light emission. Accordingly, the output values of pixel signals included in rows lower than a center row exceed the dynamic range, and then the detection value thereof is clipped. Consequently, in a graph representing a difference detection value that is the difference between the detection value at the time of preliminary light emission D2 and the detection value prior to preliminary light emission D1, the amount of reflected light actually caused by the preliminary light emission does not appear in an area in which the detection value is clipped. Thus, the amount of light required for main light emission cannot be accurately acquired only by causing all pixels to be simultaneously exposed to light.
In order to overcome the above-described difficulty, in this embodiment, electric charges are transferred from the light-receiving units 41 to the column 42 thinning out pixels so as to shorten the pixel signal read-out time of a whole image area, whereby the effect of external light applied to the computation of the amount of light required for main light emission can be reduced.
In
In
In
As described previously, in an image pickup apparatus according to this embodiment, when the preliminary light emission of the flash is performed, the exposure operations of all pixels included in the image pickup device 13 are simultaneously started, and, in addition, detection is performed by intermittently reading out an electric charge from one out of every n pixels. Accordingly, the time taken to expose the whole image area of the image pickup device 13 can be shortened, and the effect of the preliminary light emission can be applied to the whole image area of the image pickup device 13. Even if the amount of external light is relatively large, the amount of light received by the image pickup device 13 rarely exceeds the dynamic range thereof. Accordingly, the accuracy of a detection value can be improved, and the amount of light required for main light emission can be therefore more accurately computed.
Furthermore, a detection value prior to the preliminary light emission is detected in addition to a detection value at the time of preliminary light emission. By subtracting the detection value prior to preliminary light emission from the detection value at the time of preliminary light emission, a difference detection value including only the amount of light caused by the preliminary light emission except for the amount of external light can be acquired. Accordingly, the amount of light required for main light emission can be more accurately computed.
Here, a pixel thinning rate (n) may be changed in accordance with the amount of external light detected when the detection prior to preliminary light emission or the detection at the time of preliminary light emission is performed. For example, the electric charge read-out time of the whole image area is shortened by increasing the pixel thinning rate (n). Accordingly, the rate of increase of a detection value, which is changed in accordance with the position of a pixel in an image area, is more decreased in the detection value prior to preliminary light emission D1. That is, when the amount of external light is large, the portion of the detection value can be prevented from being clipped with certainty by increasing the pixel thinning rate (n).
Furthermore, if an image pickup apparatus has a zoom function achieved by lens movement, the pixel thinning rate (n) may be changed in accordance with a focal length. The reason is that, when a zoom factor is increased, the amount of light required for main light emission can be accurately computed even if the number of pixels to be detected is more decreased compared with a case in which the zoom factor is low according to a subject toward which a flash is to be fired.
Here, a human face is assumed as a subject 2. In
Here, for example, as shown in
As an example, if n=16 and the total number of rows of the image pickup device 13 is 500, a pixel area upon which the intermittent read-out operation is to be performed covers approximately 3 percent of the whole image area. If the distance L between the image pickup device 13 and the subject 2 is 2.5 m, the component of reflected light is read out at approximately 5 cm intervals on the subject 2. If the distance between a chin and forehead is 20 cm, about three or four rows are detected on a human face. If n=4, the component of reflected light is similarly read out at approximately 1 cm intervals on the subject 2.
Thus, the thinning rate (n) can be decided on the basis of the number of rows of the image pickup device 13, the focal length f, and the assumed size of a subject (here, a vertical length). Accordingly, for example, the thinning rate (n) at a wide angle end is set for each operation mode such as a portrait mode in advance. When the focal length f is increased in flash photography (i.e., a zoom factor is increased), the thinning rate (n) is caused to be increased, whereby the exposure time at the time of preliminary light emission can be shortened, and the computation accuracy of the amount of light required for main light emission can be enhanced.
An embodiment of the present invention can be applied to not only an image pickup apparatus such as a digital still camera or a digital video camera that has a still image pickup function but also a mobile telephone, a PDA (Personal Digital Assistant), etc. which have the same function.
In addition, an embodiment of the present invention can be applied to an information processing apparatus (computer) such as a personal computer capable of receiving an captured image by controlling the image pickup operations of an image pickup device and a flash which are externally connected thereto. In this case, a program in which the details of processing functions required for the above-described image pickup apparatus are written is provided for the computer. Subsequently, the computer executes the program, whereby the above-described processing functions can be achieved in the computer. The program in which the details of the processing functions are written may be stored on a computer readable recording medium. The computer readable recording medium may be a magnetic recorder, an optical disc, a magneto-optical disk, or a semiconductor memory.
If the program is distributed, for example, portable recording media with the program recorded thereon, such as an optical disc, are sold. Also, the program may be stored in the storage unit of a server computer, and may be transmitted via a network from the server computer to other computers.
The computer executing the program, for example, stores the program stored in the portable recording medium or transmitted from the server computer in its own storage unit. The computer reads out the program from its own storage unit and performs processing in accordance with the program. The computer may read out the program directly from the portable recording medium to perform processing in accordance with the program. The computer may perform processing in accordance with the received program every time the program is transmitted from the server computer.
INDUSTRIAL APPLICABILITYAccording to an embodiment of the present invention, when the preliminary light emission of a flash is performed, after the exposure operations of all pixels included in a solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals. Consequently, the effect of the preliminary light emission is applied to the whole image area of the solid-state image pickup device. In addition, since the exposure time of the solid-state image pickup device is shortened at the time of the preliminary light emission, the detected amount of the component of external light is decreased. Accordingly, even if external light is relatively strong, the amount of light detected at the time of the preliminary light emission rarely exceeds the dynamic range of the solid-state image pickup device. Therefore, the amount of the component of reflected light caused by the preliminary light emission can be accurately detected, and the accuracy of the computation of the amount of light required for main light emission can be improved, whereby a higher-quality image can be obtained.
Claims
1. An image pickup apparatus for capturing an image using a solid-state image pickup device in which the pixel signals of individual pixels can be randomly accessed, the image pickup apparatus comprising:
- a flash for exposing a subject to light;
- detecting means for detecting the brightness level of a captured image from an image signal obtained by the solid-state image pickup device; and
- controlling means for causing the flash to perform preliminary light emission prior to the main light emission of the flash, causing the solid-state image pickup device to capture an image at the time of the preliminary light emission, causing the detecting means to detect the brightness level of the image captured at the time of the preliminary light emission on the basis of the signal of the captured image, and computing the amount of light required for the main light emission of the flash on the basis of the detected brightness level at the time of the preliminary light emission, and
- wherein, the controlling means intermittently reads out the pixel signals of individual pixels at predetermined pixel intervals after causing the solid-state image pickup device to simultaneously start the exposure operations of all pixels included therein at the time of the preliminary light emission, and then transmits the read out pixel signals to the detecting means.
2. The image pickup apparatus according to claim 1,
- wherein the controlling means causes the solid-state image pickup device to capture an image without firing the flash immediately before the preliminary light emission, causes the detecting means to detect the brightness level of the image captured immediately before the preliminary light emission on the basis of the signal of the captured image, and computes the amount of light required for the main light emission of the flash on the basis of a difference value that is a difference between the brightness level detected immediately before the preliminary light emission and the brightness level detected at the time of the preliminary light emission, and
- wherein, when the solid-state image pickup device captures the image immediately before the preliminary light emission, the controlling means intermittently reads out the pixel signals of individual pixels at predetermined pixel intervals after causing the solid-state image pickup device to simultaneously start the exposure operations of all the pixels included in the solid-state image pickup device, and then transmits the read out pixel signals to the detecting means.
3. The image pickup apparatus according to claim 2,
- wherein, when the image capturing operations immediately before the preliminary light emission and at the time of the preliminary light emission are individually performed, the controlling means reads out the pixel signals included in the solid-state image pickup device in units of horizontal pixel rows.
4. The image pickup apparatus according to claim 2,
- wherein, when the image capturing operations immediately before the preliminary light emission and at the time of the preliminary light emission are individually performed, the controlling means reads out the pixel signals included in the solid-state image pickup device in units of vertical pixel columns.
5. The image pickup apparatus according to claim 2,
- wherein, when the image capturing operations immediately before the preliminary light emission and at the time of the preliminary light emission are individually performed, as the amount of external light becomes larger, the controlling means increases the pixel intervals at which the pixel signals are intermittently read out from the solid-state image pickup device.
6. The image pickup apparatus according to claim 2,
- further comprising a zoom mechanism for capturing the enlarged image of a subject by moving a lens along an optical axis, and
- wherein, when the image capturing operations immediately before the preliminary light emission and at the time of the preliminary light emission are individually performed, as the focal length of the zoom mechanism becomes longer, the controlling means increases the pixel intervals at which the pixel signals are intermittently read out from the solid-state image pickup device.
7. The image pickup apparatus according to claim 2,
- further comprising storing means for storing information on an image captured by the solid-state image pickup device before the preliminary light emission is performed, and
- wherein, when the solid-state image pickup device starts the image capturing operation immediately before the preliminary light emission, the controlling means reads out the image information stored in the storing means instead of images captured in the image capturing operations performed immediately before the preliminary light emission and at the time of the preliminary light emission, and outputs the read out image information to a subsequent image display processing device.
8. The image pickup apparatus according to claim 1,
- wherein the solid-state image pickup device is configured with an XY address type image sensor.
9. The image pickup apparatus according to claim 8,
- wherein the XY address type image sensor is configured with a CMOS image sensor.
10. An image pickup method of capturing an image by firing a flash using a solid-sate image pickup device in which the pixel signals of individual pixels can be randomly accessed, the image pickup method comprising:
- an image capturing step at the time of preliminary light emission of causing the flash to perform preliminary light emission prior to the main light emission of the flash, and causing the solid-state image pickup device to capture an image at the time of the preliminary light emission;
- a detecting step at the time of preliminary light emission of causing detecting means to detect the brightness level of the image captured at the time of the preliminary light emission; and
- a computing step of causing computing means to compute the amount of light required for the main light emission of the flash on the basis of the brightness level detected at the time of the preliminary light emission, and
- wherein, in the image capturing step at the time of preliminary light emission, after the exposure operations of all pixels included in the solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals.
11. The image pickup method according to claim 10, further comprising:
- an image capturing step prior to preliminary light emission of causing the solid-state image pickup device to capture an image without firing the flash before the image capturing step at the time of preliminary light emission; and
- a detecting step prior to preliminary light emission of causing the detecting means to detect the brightness level of the image captured in the image capturing step prior to preliminary light emission on the basis of the signal of the captured image, and
- wherein, in the image capturing step prior to preliminary light emission, after the exposure operations of all the pixels included in the solid-state image pickup device have been simultaneously started, the pixel signals of individual pixels are intermittently read out at predetermined pixel intervals, and
- wherein, in the computing step, the amount of light required for the main light emission of the flash is computed on the basis of a difference value that is a difference between the brightness level detected in the detecting step prior to preliminary light emission and the brightness level detected in the detecting step at the time of preliminary light emission.
12. An image pickup control program causing a computer to perform image pickup control processing for capturing an image by firing a flash using a solid-state image pickup device in which the pixel signals of individual pixels can be randomly accessed, the image pickup control program causing the computer to function as:
- controlling means for causing the flash to perform preliminary light emission prior to the main light emission of the flash, causing the solid-state image pickup device to capture an image at the time of the preliminary light emission, causing detecting means to detect the brightness level of the image captured at the time of the preliminary light emission on the basis of the signal of the captured image, and intermittently reading out the pixel signals of individual pixels at predetermined pixel intervals after causing the solid-state image pickup device to simultaneously start the exposure operations of all pixels included in the solid-state image pickup at the time of the preliminary light emission; and
- computing means for computing the amount of light required for the main light emission of the flash on the basis of the brightness level detected by the detecting means at the time of the preliminary light emission.
13. The image pickup control program according to claim 12,
- wherein the controlling means causes the solid-state image pickup device to capture an image without firing the flash immediately before the preliminary light emission, causes the detecting means to detect the brightness level of the image captured immediately before the preliminary light emission on the basis of the signal of the captured image, and
- wherein the computing means computes the amount of light required for the main light emission of the flash on the basis of a difference value that is a difference between the brightness levels detected by the detecting means immediately before the preliminary light emission and at the time of the preliminary light emission, and
- wherein, when the solid-state image pickup device captures the image immediately before the preliminary light emission, the controlling means intermittently reads out the pixel signals of individual pixels at predetermined pixel intervals after causing the solid-state image pickup device to simultaneously start the exposure operations of all the pixels included in the solid-state image pickup device.
Type: Application
Filed: Aug 4, 2005
Publication Date: Aug 27, 2009
Patent Grant number: 7834931
Inventors: Kazato Tanaka (Tokyo), Takuya Chiba (Tokyo), Naoki Hayashi (Chiba)
Application Number: 11/659,234
International Classification: H04N 5/262 (20060101); H04N 5/235 (20060101); H04N 5/335 (20060101);